AMD, mixed-master-type provisioning

[bengland2]

JetSki failed (master branch as of Nov 30 9 AM) when run on an AMD server reservation in Alias consisting of 7425 and 7525 server types. Initially this was because of undefined variable errors in roles/bootstrap/tasks/10_load_inv.yml for list variables describing the cluster members. I fixed this by removing the default filter from the set_fact statements for these vars, and adding a set_fact statement that initialized them all to the empty list.

However, then it would still fail because it did not recognize the servers as Dells. So I added these machine types (first commit) in roles/bootstrap/defaults/main.yml .

The last failure was caused by check for non-homogeneity of master server machine types and provisioner machine type. I removed this constraint for now because it was too tight - is this constraint necessary?

A corresponding PR is being added so people can review my code.